1. Field of the Invention
This invention relates to Nuclear Magnetic Resonance (NMR) spectroscopy of a sample and more particularly NMR spectroscopy of constituents of a fluid sample moving at a predetermined velocities.
2. Description of Related Art
NMR spectroscopy procedures are used routinely to determine molecular structure, analyze mixtures and quantify concentrations of substances in a sample. Modern NMR methods provide information about a sample by the direct or indirect detection of one or more intrinsic parameters as described in Modern NMR Spectroscopy by J. K. M Sanders, and B. K. Hunter, Chapters 1.1, 1.2, 1.4 and 6.2 Oxford Univ. Press 1987 Oxford, England, New York, N.Y., Tokyo, Japan, hereby incorporated by reference. Among these parameters are: 1) chemical shift which arises from the local magnetic fields surrounding the nuclear spin caused by electronic bonds which connect the atoms within the molecule, 2) spin-spin coupling which arises from interactions of non-equivalent nuclear spins, 3) spin-lattice relaxation of longitudinal spin magnetization which is typically dominated by molecular motion within the main magnetic field, 4) spin-spin relaxation which manifests itself as an non-reversible loss of transverse spin coherence arising from the interaction of nuclear spins in non-equivalent spin states, 5) Nuclear-Overhauser effects which cause changes in longitudinal spin magnetization through interactions of spins having different gyromagnetic ratios, and 6 ) Multiple quantum effects arising from the concerted flipping of more than one spin in a system of coupled spins.
Although spin-spin interactions and spin-lattice interactions are influenced by the rate of molecular tumbling, and thus are somewhat sensitive to molecular weight, the use of these intrinsic parameters for qualitative molecular weight determination is rare, particularly when other intrinsic parameters are being measured.
Often it is desirable to use NMR methods to determine the components of a mixture. Mixtures of relatively small molecules can be readily analyzed with single dimension procedures provided that each component is unambiguously represented in some portion of the acquired data. Larger molecules having more complicated spectra, or mixtures of similar molecules, require NMR procedures which exploit additional intrinsic parameters. These procedures typically require the acquisition of data in two or more dimensions. Unfortunately, analysis of a mixture into its components is not guaranteed and separation of NMR spectra by an additional intrinsic parameter is frequently desirable.